1. Field of the Invention
The present invention relates to mask pattern transfer lithography technique in manufacturing a semiconductor integrated circuit or a crystal panel, and more particularly to a method of manufacturing a semiconductor device using a stencil mask having an opening (through hole) pattern.
2. Prior Art
In lithography technique used for forming patterns of semiconductor integrated circuits or the like, electron beam projection and exposure has been studied in which a mask is irradiated with a uniform electron beam and the electron beam passing through the mask is projected on a wafer by an electron optical system. Electron beam projection and exposure technique is described in Japanese Journal of Applied Physics vol. 34 (1995), pp. 6658-6662, Japanese Journal of Applied Physics vol. 34 (1995), pp. 6663-6671, and Japanese Journal of Applied Physics vol. 39 (2000), pp. 6897-6901.
The mask used in this electron beam projection and exposure technique includes a transmission area that transmits the electron beam and has an electron beam image of a desired pattern shape reach on a wafer, and a scattering area that disperses the electron beam and prevents the electron beam from reaching on the wafer.
Mask structures invented are a membrane type mask having a thin film remain on the electron beam transmission area, and a stencil type mask having no thin film remain to form an opening. The membrane mask has at least the thin film throughout the mask, so that existence of an electron beam dispersion area (doughnut pattern) completely surrounded by the electron beam transmission area causes no problem. However, the electron beam transmission area has the thin film, and thus energy loss of the transmission electron beam causes chromatic aberration to thereby cause a problem of degradation of a transfer pattern shape. In the stencil mask, an electron beam transmitting portion is an opening to thereby prevent the degradation of the transfer pattern due to the chromatic aberration. However, when the doughnut pattern exists, the stencil mask cannot support electron beam dispersion area surrounded by an electron beam transmission, and thus technique has been proposed in which the doughnut pattern is divided into two parts and a mask is divided into two masks (complementary masks) having the respective parts for transfer.
The complementary mask has an object to solve the problem of the doughnut pattern, and also has an advantage of preventing degradation in pattern accuracy due to Coulomb effect by a uniform mask opening ratio for each predetermined area.
For the complementary mask division, JP-A-11-135417 specification discloses that a bending portion is a dividing boundary.
48th Japan Society of Applied Physics Academic Lecture Preliminary Report (March 2001, Meiji University), No. 2, p. 747 discloses that a doughnut pattern, leaf like pattern and L shaped pattern are extracted/divided, and the other patterns are also divided so as to have substantially equal area ratios after the complementary mask division.
JP-A-11-135417 specification does not disclose in detail methods of corner extraction from layout data and generation of two mask data. When an elongate dispersion area is between the openings, it is preferable that the dispersion area is divided into parts to use complementary masks having the respective parts in order to prevent mask deformation, but the document does not consider flexion of the mask at an opening of a long side.
In the technique described in 48th Japan Society of Applied Physics Academic Lecture Preliminary Report (March 2001, Meiji University), No. 2, p. 747, a dividing boundary of a pattern is only a line parallel to the y axis as is apparent from a drawing in the document, and a narrow slit like pattern is generated in a step like pattern portion where the y coordinate gradually changes as shown in FIG. 17. This is a significant factor of degradation in EB drawing accuracy in mask fabrication like a problem of a minute pattern in EB data generation. The above described document has no description on alignment error.
Although it is described that the patterns are divided so as to have substantially equal area ratios, there is no description on a range of the equal area ratios. The complementary masks have the equal area ratios because the Coulomb effect that may cause degradation of a focusing pattern has equal influences on two complementary masks.
However, in the known examples, when an area ratio of an upper half of a subfield (an area that can be irradiated with an electron beam at once) of one mask after division is 50% and an area ratio of a lower half is 5%, an area ratio of the entire subfield is 30% and less, but there is a problem that resolution is locally degraded in the upper half due to the Coulomb effect. From the inventors"" studies, this may be because an influence range of the Coulomb effect (hereinafter referred to as Coulomb effect influence range) is smaller than the subfield. The Coulomb effect influence range depends on an optical system, and may be, for example, about {fraction (1/10)} or less of one side of the subfield.
An object of the present invention is to provide a method of manufacturing a semiconductor device capable of forming a fine pattern with high accuracy using a complementary mask.
Outlines of representative aspects of the invention disclosed in this application are as follows:
Input layout data is classified into a rectangle having a width within a certain range, a boundary is created in accordance with a reference point provided for each classified rectangles, the input layout data is divided into fractionized patterns using the boundary, and the fractionized patterns adjacent to each other via the boundary are distributed into two masks so as to be in different masks. The boundary may be created in any of an x axis direction or a y axis direction. The boundary may be a boundary line or a boundary figure having an area.
A doughnut pattern can be surely divided into a set of rectangles and thus can be divided into two masks. Appropriately setting a dividing length of a rectangle can prevent generation of an elongate dispersion portion between openings.
When the boundary is a figure with an area, the boundary figure is included in both of the complementary masks to prevent breaking of a wire when alignment error occurs. If the distributed fractionized patterns and boundary figures are output in different layers, it is easy to increase overlap between the complementary masks for preventing the alignment error by enlarging the boundary figure and operating OR with the complementary layers. Thus data can be generated with a large alignment margin without generating again the complementary mask data from the beginning.
In the layout data for the complementary mask generated by the layout data dividing method for the complementary mask as described above, a pattern area ratio within a range influenced by the Coulomb effect around any chosen position of each complementary layer is less than a predetermined value. Specifically, the area ratio within the range influenced by the Coulomb effect is preferably 30% and less. The Coulomb effect influence range depends on an electron optical system, but may be typically 10 to 50 xcexcm. Pattern degradation due to the Coulomb effect may be prevented if the area ratio within the Coulomb effect influence range is 20% to 40%. This is not the case when no fine pattern influenced by the Coulomb effect exists. Specifically, a dimension dividing reference unit when the input data in the form of fractionized patterns is distributed into the complementary layers are set sufficiently smaller than a property length influenced by the Coulomb effect depending on the pattern shapes, and thus the area ratio within the Coulomb effect influence range around any chosen point of the complementary layer can be divided into equal parts for each complementary layer or can be less than a predetermined value in each complementary layer. Therefore, influence on resolution of the Coulomb effect is smaller than a certain value in any areas where the Coulomb effect locally occurs on the mask, thus obtaining a desired resolution.
When a gate of an MOS transistor is formed by optical lithography, in order to generate a phase shift mask pattern for exposing both sides of the gate to light of substantially opposite phases, a pattern operation tool is used that has a function of outputting patterns on both sides of a gate pattern as in different layers, and with the pattern to be divided by the boundary (the sum of the area of the fractionized patterns on both sides of the boundary and the boundary) and the boundary over the pattern, the fractionized patterns on both sides of the boundary are determined as a first complementary layer and a second complementary layer, respectively.
There can be provided a method of manufacturing a semiconductor device capable of forming a fine pattern with high accuracy using a complementary mask having no elongate electron-scattering portion between the openings that may cause flexion of the mask and a complementary mask in which no pattern degradation occurs due to the alignment error resulting from double exposure. Using the complementary mask can eliminate the doughnut pattern, and a uniform mask opening ratio for each predetermined area can further increase dimensional accuracy.
In the Coulomb effect influence range, dividing the pattern into the complementary mask in such a manner that a maximum area ratio of the mask is within a certain limit is advantageous for pattern dimensional accuracy.
Further, the complementary mask data can be automatically obtained at high speed using an existing pattern operation tool with respect to any chosen layout pattern data. That is, there may be no need for developing a new special program requiring development hours in order to generate such complementary mask data.
Other objects, features, and advantages of the invention will be apparent from the following description of embodiments of the invention with reference to the accompanying drawings.